Hello all, this may be old news to some of you SC400 owners. I have seen many post on the subject of engine hesitation. I too have had a very bad hesitation starting around 1600rpms up to around 2800rpms. After that the engine would run fine. The hesitation and or bucking was VERY bad. My issue would start out with the engine starting just fine and idling just fine with NO ECU codes. After driving the car less then a block I would get a CEL, and the code being 52, knock sensor. I check many thing over a couple of months. MAF was thought to be a issue as when you disconnect it the engine would run great. All engine sensors were checked over and over, with a ohm meter at the ECU connect. Engine temp, MAF, cam 1 and cam2 sensors, crank sensors, fule pump, even the O2's as best I could. NO sensors really showed to be bad. I used a analog scope to look at most of these sensors, I could watch the cam's1 and 2 with the crank all line up on the scope, at any RPM. I took a chance changing the MAF out with a unit I bought online from China, it worked good, but not the issue.
After many many hours of trying to understand what the ECU might be seeing that it just did not like, and probing all the sensor signals coming into the computer, I figured it was worth a chance to change the ECU. I found a nice parts guy local and he had a used 95 ECU. I tried it and it fixed ALL issues.
Its kinda funny, this car has had a very small hesitaion for over 10 years, but no one could find it, incuding the lexus dealer. I hope this helps someone that might be having a bucking or hesitation issue with the SC400. When it all the sensors check out, try the ECU, they are not that expensive and is worth the time you will spend testing and testing and talking to repair shops that think they know the early sc400 cars.
After many many hours of trying to understand what the ECU might be seeing that it just did not like, and probing all the sensor signals coming into the computer, I figured it was worth a chance to change the ECU. I found a nice parts guy local and he had a used 95 ECU. I tried it and it fixed ALL issues.
Its kinda funny, this car has had a very small hesitaion for over 10 years, but no one could find it, incuding the lexus dealer. I hope this helps someone that might be having a bucking or hesitation issue with the SC400. When it all the sensors check out, try the ECU, they are not that expensive and is worth the time you will spend testing and testing and talking to repair shops that think they know the early sc400 cars.
